"Un-Earthing" Discoveries

Earthworm Dissection: PAP Bio - Vu 7- April 6, 2014 - J Chen

"Ground" Objectives

Students will be able to dissect an earthworm and discover the internal anatomy of an invertebrate. They will explore the earthworm's organs and understand the function(s) of each.

Back"ground" Information

The earthworm is a commonly known organism that resides mostly, as figured from its name, in the earth. It functions at its best in soil, trees, under rocks, and on the banks of streams. This worm, otherwise known as Lumbricus terrestris, feeds on soil, absorbing nutrients in the earth for food. It is preyed upon by frogs, fish, turtles, and most commonly, birds. An earthworm's niche grouping falls mainly in the compost and soil-surface dwellers and it breaks down decaying carcasses and leaves. It has adapted to its environment by growing setae, bristles on the body which help the earthworm grip and move through soil. A streamlined body, with no arms or legs, provides an additional advantage to the earthworm when snaking though soil.

The Digestive System

An earthworm's digestive system is similar to that of most organisms. The organs used in the earthworm's digestive system are the mouth, pharynx, esophagus, crop, gizzard, and intestine. The digestive system functions mainly in extracting the nutrients from the earthworm's food. The nutrients will then feed the worm, allowing it to function properly. The earthworm's sustenance first approaches the mouth. After broken into smaller pieces, the pharynx lubricates the food allowing it to travel down the earthworm's digestive tract more easily. The substance then enters the crop, where it will be mixed together. Then it enters the gizzard, where the actual digestive process will begin. Enzymes in the gizzard aid in chemical breakdown and then the mixture in sent to travel through the intestine. After the intestine and blood vessels inside the intestine absorb the nutrients, the unused matter exits the earthworm through the anus. This digestive system relates to other systems in that its function is essential in order for other systems to be able to operate. The earthworm's other body systems cannot function without nutrients processed in the digestive system.

Un"earth"ed Fun Facts

-There are approximately 6,000 earthworm species worldwide.

-Because earthworms lack lungs, they breathe through their skin.

-The earthworm does not have a specified gender; it contains both egg and sperm.

-An earthworm secretes a lubricating fluid to make burrowing easier.